Grease fittings constructed of metal are conventionally inserted in threaded bores extending through wheel hubs, as illustrated in FIG. 1 herein, for attachment to a grease applicator, such as a grease gun, to inject grease through the fitting and into the hub for lubricating bearings disposed therein. The threaded bores and the metal grease fittings add a significant extra expense to a completed wheel hub because of the extra cost for material and time required for manufacturing and assembly.
Depending on the application and manufacturing specifications, a standard wheel hub might or might not be fitted with a grease fitting. To reduce manufacturing costs, only those wheel hubs needing grease fittings are manufactured with threaded bores for grease fittings. When a grease fitting is not to be utilized, no bore is incorporated into the hub. This frequently results in a dual inventory of hubs with fittings and those without. For hubs with grease fittings, assembling the threaded fitting into the bore also adds a significant manufacturing and assembly expense.